U.S. patent application number 10/278808 was filed with the patent office on 2003-05-08 for image pick-up apparatus.
This patent application is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Nagano, Akihiko.
Application Number | 20030086008 10/278808 |
Document ID | / |
Family ID | 19157216 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030086008 |
Kind Code |
A1 |
Nagano, Akihiko |
May 8, 2003 |
Image pick-up apparatus
Abstract
An image pick-up apparatus includes a plurality of pixels, each
of which includes a photoelectrically converting area for
converting an optical signal from a subject into an electronic
signal. A plurality of first pixels included in the plurality of
pixels have a first transmittance as a light transmittance to the
photoelectrically converting area, and a plurality of second pixels
included in the plurality of pixels have a second transmittance as
a light transmittance to the photoelectrically converting area. The
second transmittance is higher than the first transmittance, and a
light receiving area for receiving light of each of the plurality
of first pixels is larger than a light receiving area for receiving
light of each pixel of the plurality of second pixels.
Inventors: |
Nagano, Akihiko; (Chiba,
JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
Canon Kabushiki Kaisha
Tokyo
JP
|
Family ID: |
19157216 |
Appl. No.: |
10/278808 |
Filed: |
October 24, 2002 |
Current U.S.
Class: |
348/272 ;
348/E9.01 |
Current CPC
Class: |
H04N 9/04555 20180801;
H04N 5/3696 20130101; H04N 9/0451 20180801; H04N 9/04557
20180801 |
Class at
Publication: |
348/272 |
International
Class: |
H04N 005/335 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2001 |
JP |
2001-343546 |
Claims
What is claimed is:
1. An image pick-up apparatus, comprising a plurality of pixels,
each of said pixels including a photoelectrically converting area
for converting an optical signal from a subject into an electronic
signal, wherein a plurality of first pixels included in said
plurality of pixels have a first transmittance as a light
transmittance to said photoelectrically converting area, a
plurality of second pixels included in said plurality of pixels
have a second transmittance as a light transmittance to said
photoelectrically converting area, the second transmittance being
higher than the first transmittance, and a light receiving area for
receiving light of the first pixel of said plurality of first
pixels is larger than a light receiving area for receiving light of
a second pixel of said plurality of second pixels.
2. An apparatus according to claim 1, further comprising a control
circuit which forms an image based on the electronic signal from
said first pixel and detects a focal point based on the electronic
signal from said second pixel.
3. An apparatus according to claim 1, wherein said plurality of
first pixels have a pixel to which a red transmitting filter is
arranged, pixels to which a blue transmitting filter is arranged,
and pixels to which a green transmitting filter is arrangement.
4. An apparatus according to claim 3, wherein said plurality of
pixels have a first diagonal alignment of pixels to which said red
transmitting filter is arranged and of pixels to which said blue
transmitting filter is arranged, and a second diagonal alignment of
pixels to which said green transmitting filter is arranged and of
pixels having said first pixel, intersecting said first diagonal
alignment.
5. An apparatus according to claim 1, wherein said first pixel has
a plurality of photoelectrically converting areas, a common
amplifying device which amplifies and outputs signals from said
plurality of photoelectrically converting areas, and a plurality of
first transfer switches which connect said common amplifying device
to said plurality of photoelectrically converting areas, said
second pixel has an amplifying device which amplifies and outputs
signals from said photoelectrically converting areas and a second
transfer switch which connects said photoelectrically converting
areas to said amplifying device, and said apparatus further
comprises: a third transfer switch which transfers the signal from
said photoelectrically converting area included in said first pixel
to said amplifying device included in said second pixel; and a
driving circuit having a first mode in which an input unit in said
amplifying device mixes the signals from said plurality of
photoelectrically converting areas included in said first pixel and
a mixed signal is read from said amplifying device, and a second
mode in which the signal from one photoelectrically converting area
among said plurality of photoelectrically converting areas included
in said first pixel is read from said amplifying device included in
said first pixel and the signal from another photoelectrically
converting area among said plurality of photoelectrically
converting areas included in said first pixel is read from said
amplifying device included in said second pixel.
6. An apparatus according to claim 5further comprising: a control
circuit which forms an image based on the signal read in said first
mode and detects a focal point based on the signal read in said
second mode.
7. An image pick-up apparatus comprising: a plurality of pixels
including a first pixel and a second pixel, said first pixel having
a plurality of photoelectrically converting areas, a common
amplifying device for amplifying and outputting signals from said
plurality of photoelectrically converting areas, and a plurality of
first transfer switches for connecting said common amplifying
device to said plurality of photoelectrically converting areas,
said second pixel having at least a photoelectrically converting
area, an amplifying device for amplifying and outputting a signal
from said photoelectrically converting area, and a second transfer
switch for connecting said photoelectrically converting area to
said amplifying device; and a third switch for transferring the
signal from said photoelectrically converting area included in said
first pixel to said amplifying device included in said second
pixel.
8. An apparatus according to claim 7, further comprising: a driving
circuit having a first mode in which an input unit in said
amplifying device mixes the signals from said plurality of
photoelectrically converting areas included in said first pixel and
a mixed signal is read from said amplifying device, and a-second
mode in which the signal from one photoelectrically converting area
among said plurality of photoelectrically converting areas included
in said first pixel is read from said amplifying device included in
said first pixel and the signal from another photoelectrically
converting area among said plurality of photoelectrically
converting areas included in said first pixel is read from said
amplifying device included in said second pixel.
9. An apparatus according to claim 8, further comprising: a control
circuit which forms an image based on the signal read in said first
mode and detects a focal point based on the signal read in said
second mode.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an image pick-up apparatus
for picking up an image of a subject.
[0003] 2. Description of the Related Art
[0004] Hitherto, image pick-up apparatuses for a digital camera and
the like comprise color filters which are arranged between
two-dimensionally arranged pixels and an image pick-up lens for
condensing light from a subject so as to obtain a color image.
[0005] FIG. 17 is a schematic diagram of the conventional
arrangement of color filters. Herein, a Bayer arrangement is shown.
Reference symbols R, G, and B denote a red transmitting filter, a
green transmitting filter, and a blue transmitting filter,
respectively.
[0006] Referring to FIG. 17, an image pick-up operation and an the
operation for detecting a focal point is performed by using a
signal from the image pick-up apparatus having the arrangement of
color filters shown in FIG. 17.
[0007] However, in the conventional art, the color filters are
arranged to obtain a color image, and therefore the signal level
output from each pixel is lower than that in the case of no
arrangement of the color filters. More specifically, the signal
level with the color filters is approximately 1/3 of that in the
case of no arrangement of the color filters.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the present invention to
provide an image pick-up apparatus which can perform both an image
pick-up operation and an operation for detecting a focal point.
[0009] In order to accomplish the above-mentioned object, according
to one aspect of the present invention, there is provided an image
pick-up apparatus, comprising a plurality of pixels, each of the
pixels including a photoelectrically converting area for converting
an optical signal from a subject into an electronic signal, wherein
a plurality of first pixels included in the plurality of pixels
have a first transmittance as a light transmittance to the
photoelectrically converting area, a plurality of second pixels
included in the plurality of pixels have a second transmittance as
a light transmittance to the photoelectrically converting area, the
second transmittance being higher than the first transmittance, and
a light receiving area for receiving light of the first pixel of
the plurality of first pixels is larger than a light receiving area
for receiving light of a second pixel of the plurality of second
pixels.
[0010] According to another aspect of the present invention, there
is provided an image pick-up apparatus comprising: a plurality of
pixels including a first pixel and a second pixel, the first pixel
having a plurality of photoelectrically converting areas, a common
amplifying device for amplifying and outputting signals from the
plurality of photoelectrically converting areas, and a plurality of
first transfer switches for connecting the common amplifying device
to the plurality of photoelectrically converting areas, the second
pixel having at least a photoelectrically converting area, an
amplifying device for amplifying and outputting a signal from the
photoelectrically converting area, and a second transfer switch for
connecting the photoelectrically converting area to the amplifying
device; and a third switch for transferring the signal from the
photoelectrically converting area included in the first pixel to
the amplifying device included in the second pixel.
[0011] Further objects, features and advantages of the present
invention will become apparent from the following description of
the preferred embodiments (with reference to the attached
drawings).
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a block diagram of the schematic structure of a
digital still camera according to a first embodiment of the present
invention;
[0013] FIG. 2 is a plan view of the schematic structure of an image
sensor in FIG. 1;
[0014] FIGS. 3A and 3B are enlargement views of pixels (0, 0) and
(1, 0) in FIG. 2;
[0015] FIG. 4 is a flowchart showing the operation of the digital
still camera 1 in FIG. 1;
[0016] FIGS. 5A and 5B are explanatory diagrams of pixels of a
digital still camera according to a second embodiment of the
present invention;
[0017] FIG. 6 is a flowchart showing the sequence of the adjustment
of the luminance by the digital still camera having color filters
shown in FIG. 5B;
[0018] FIG. 7 is a block diagram showing the schematic structure of
a digital still camera according to a third embodiment of the
present invention;
[0019] FIG. 8 is a plan view showing the schematic structure of an
image sensor in FIG. 7;
[0020] FIGS. 9A to 9C are enlargement views of pixels (2,0), (0,2),
and (1,0) in FIG. 8;
[0021] FIG. 10 is a cross-sectional view of the image sensor in
FIG. 7;
[0022] FIG. 11 is a circuitry diagram including the image sensor in
FIG. 7;
[0023] FIGS. 12A and 12B are timing charts showing the operation of
circuits in the image sensor in FIG. 11;
[0024] FIG. 13 is a flowchart showing the operation of the digital
still camera in FIG. 7;
[0025] FIG. 14 is a flowchart showing the sequence for calculating
a luminance signal to adjust the luminance by an image processing
circuit in FIG. 7;
[0026] FIG. 15 is a plan view showing an example of a hexangular
pixel in FIG. 2;
[0027] FIG. 16 is a cross-sectional view of an image sensor in FIG.
1; and
[0028] FIG. 17 is a schematic diagram of the conventional
arrangement of color filters.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Hereinbelow, embodiments of the present invention will be
described with reference to the drawings.
[0030] (First Embodiment)
[0031] FIG. 1 is a block diagram showing the schematic structure of
a digital still camera 1 according to the first embodiment of the
present invention. Referring to FIG. 1, the digital still camera 1
comprises a photographing lens 5 including a convex lens 5a, a
concave lens 5b, and a stop 53, which condenses light from a
subject, a photographing lens driver 51 for moving the
photographing lens 5, an image sensor 10 arranged to a prearranged
image forming surface of the photographing lens 5, an image sensor
control circuit 21 for controlling the driving of the image sensor
10, an image processing circuit 24 for processing an image signal
from the image sensor 10, a liquid crystal display device 9 for
displaying the image processed by the image processing circuit 24,
a liquid crystal display driving circuit 25 for driving the liquid
crystal display device 9, an eye piece 3 for viewing an image of
the subject displayed on the liquid crystal display device 9, a
memory circuit 22 for recording the image signal from the image
sensor 10, an interface circuit 23 for outputting the image
processed by the image processing circuit 24 to the outside of the
digital still camera 1, and a CPU 20 for controlling the operations
of the image sensor control circuit 21, the memory circuit 22, the
interface circuit 23, and the image processing circuits 24 and 51
and performing the calculation for the detection of the focal
point.
[0032] As shown in FIG. 1, the photographing lens 5 is shown
comprising two lenses, photographing lens 5 may convex lens 5a and
concave lens 5b; however, actually comprises a number of lenses as
be known in the art.
[0033] FIG. 2 is a plan view of the schematic structure of the
image sensor 10 in FIG. 1. Referring to FIG. 2, pixels with six
rows and six columns are aligned. However, the pixels corresponding
to the use are actually aligned. Reference symbols "R", "G", and
"B" denote the color of red, green, and blue color filters of the
pixels. The same color pixels are aligned with grid patterns to
improve the resolution of the picked-up image.
[0034] Herein, the arrangement of the pixels is similar to the
Bayer arrangement. Differently from the Bayer arrangement, the
number of "G" is small. Therefore, upon normal-image pick-up
operation, a color difference signal is output by "R", "G", and "B"
pixel outputs, and a luminance signal is generated by the output of
the pixel to which the color filter is not formed (that is, the
pixel without the color filter).
[0035] Referring to FIG. 15, the shape of the pixel may be
hexangular and may have an arrangement similar to that different
from the Bayer arrangement.
[0036] FIGS. 3A and 3B are enlargement views of pixels (0, 0) and
(1, 0) in FIG. 2. The pixels (0, 0) and (1, 0) comprise
photoelectrically converting units S.sub.B and S.sub.W,
respectively. Referring to FIGS. 3A and 3B, an area of the
photoelectrically converting unit S.sub.B in the pixel (0, 0) is
larger than that of the photoelectrically converting unit SW in the
pixel (1, 0).
[0037] According to the first embodiment, areas of
photoelectrically converting units S.sub.G and S.sub.R of the
pixels (0, 1) and (1, 1) are equal to the area of the
photoelectrically converting unit S.sub.B. However, they may be
changed depending on the difference of the output levels of R, G,
and B. Incidentally, the area of the photoelectrically converting
unit means an area of a photoelectrically converting region for
substantially photoelectrical conversion determined depending on a
numerical aperture of the pixel.
[0038] Herein, the area of the photoelectrically converting unit
S.sub.W is smaller than those of the remaining photoelectrically
converting units S.sub.G, S.sub.R, and S.sub.B for the purpose of
preventing the saturation of stored charges which is caused by the
pixel (0, 0) having a higher light receiving efficiency as compared
with other pixels.
[0039] Ratios of the photoelectrically converting units S.sub.G,
S.sub.R, and S.sub.B to the photoelectrically converting units
S.sub.W are determined depending on light transmittances. Since the
light transmittance of the color filter is about 1/3, the area of
the photoelectrically converting units S.sub.W is about 1/3 of the
individual areas of the photoelectrically converting units S.sub.G,
S.sub.R, and S.sub.B.
[0040] If the area of the photoelectrically converting units
S.sub.W is smaller than 1/3 of the individual areas of the
photoelectrically converting units S.sub.G, S.sub.R, and S.sub.B,
an image with a high S/N ratio cannot be obtained in the case of
the subject with a low luminance. Therefore, the area of the
photoelectrically converting units SW is actually 1/3 or more of
the individual areas of the photoelectrically converting units
S.sub.G, S.sub.R, and S.sub.B.
[0041] In summary, according to the first embodiment, the areas of
the photoelectrically converting units S.sub.W, S.sub.G, S.sub.R,
and S.sub.B are as follows.
[0042] S.sub.B=S.sub.G=S.sub.R
[0043] S.sub.B>S.sub.W.gtoreq.S.sub.B/3
[0044] FIG. 16 is a cross-sectional view of the image sensor 10 in
FIG. 1. Referring to FIG. 16, the image sensor 10 comprises a CMOS
image sensor. Herein, the cross-sectional views of the pixels in
FIGS. 3A and 3B are shown.
[0045] Reference numeral 117 denotes a P-type well, and reference
numeral 118 denotes a SiO.sub.2 film as an MOS gate insulating
film. Reference numerals 126.sub.G and 126.sub.W denote surface
P.sup.+ layers, and form n layers 125.sub.G and 125.sub.W and
photoelectrically converting units 101.sub.G and 101.sub.W,
respectively.
[0046] Reference numerals 120.sub.G and 120.sub.W denote transfer
gates for transferring optical charges stored in the
photoelectrically converting units 101.sub.G and 101.sub.W to
floating diffusion unit (hereinafter, referred to as FD unit)
121.
[0047] Further, reference numeral 129 denotes the color filter, and
reference numeral 130 denotes a micro lens. Each micro lens 130 is
formed at a position and a the shape in which the pupil of the
photographing lens 5 and the photoelectrically converting unit 101
of the image sensor 10 are conjugate.
[0048] The FD unit 121 is arranged on the pixel (1, 0) side. Since
the n-layer 125.sub.W is smaller than the n-layer 125.sub.G, the FD
units 121 are formed near the n-layer 125.sub.W and the size of the
image sensor 10 can be decreased. Incidentally, the FD unit 121 is
formed between the pixels (0, 1) and (1, 1) and the pixel (1, 0).
These FD units 121 are arranged on the pixel (1, 0) side.
[0049] FIG. 4 is a flowchart showing the operation of the digital
still camera 1 in FIG. 1.
[0050] A photographing person switches on a main switch (not shown)
of the digital still camera 1 in FIG. 1 (step S201). Then, the CPU
20 sends a control signal to the image sensor control circuit 21
and picks up an image for display operation on the image sensor 10
and for focus detection (step S202).
[0051] The image signal which is picked up by the image sensor 10
is A/D converted by the image processing circuit 24 and thereafter
is subjected to image processing. In this case, predetermined image
processing is performed based on an output signal from the image
sensor 10 for color reproduction.
[0052] The image signal which is subjected to image processing is
displayed on the liquid crystal display device 9 by the liquid
crystal display device driving circuit 25 so that the photographing
person observes the subject image via the eye piece 3 (step
S203).
[0053] Further, the CPU 20 performs a calculation for focus
detection of the photographing lens 5. The calculation is performed
based on the output of the image sensor 10 and uses a so-called
climbing type focus detecting method for searching peaks of
contrasts of the subject image (step S204).
[0054] If the photographing lens 5 is not in a focusing state, the
photographing lens 5 is driven by a predetermined amount so as to
be close to the focusing state. Specifically, the CPU 20 sends a
lens driving signal to the photographic lens driver 51 and drives
the photographing lens 5 by the predetermined amount (step
S205).
[0055] Further, the CPU 20 switches on a switch SW2 for recording
the picked-up image (step S206). Then, the CPU 20 sends a control
signal to the image sensor control circuit 21 and the image sensor
10 performs the actual image pick-up operation (step S207).
[0056] In this case, since the photoelectrically converting units
of the pixel to which the color filter is formed (that is, the
pixel with the color filter) have the same size, deterioration in
sensitivity is prevented and a color difference signal with a high
S/N ratio can be obtained.
[0057] Since the area of the photoelectrically converting unit of
the pixel to which the color filter is not formed (that is, the
pixel without the color filter) is smaller than the area of the
photoelectrically converting unit of the pixel with the color
filter, the luminance signal can also be output without saturating
the output of the pixel without the color filter in the case of a
bright subject.
[0058] The image generated by the image processing circuit 24 is
sent to the liquid crystal display device driving circuit 25 and is
displayed on the liquid crystal display device 9 (step S208).
[0059] Simultaneously, under the control of the CPU 20, the
picked-up image signal is stored in the memory circuit 22 in the
digital still camera 1 (step S209).
[0060] The photographing operation ends and the photographing
person switches off the main switch (step S210). Then, the power
source of the digital still camera 1 is turned off.
[0061] (Second Embodiment)
[0062] FIGS. 5A and 5B are explanatory diagrams of the pixels of
the digital still camera 1 according to a second embodiment of the
present invention. Referring to FIG. 5A, the pixel (0, 0) in FIG. 2
is shown. Referring to FIG. 5B, the pixel (1, 0) in FIG. 2 is
shown.
[0063] Other structure according to the second embodiment is the
same as that according to the first embodiment.
[0064] The pixel (0, 0) comprises the photoelectrically converting
unit S.sub.B. The pixel (1, 0) comprises a first photoelectrically
converting unit S.sub.W1 including the center portion and a second
photoelectrically converting unit S.sub.W2 which surrounds the
first photoelectrically converting unit S.sub.W1.
[0065] Since the pixel (1, 0) comprises the first photoelectrically
converting unit S.sub.W1 and the second photoelectrically
converting unit S.sub.W2, the luminance is adjusted based on the
signals.
[0066] The areas of the photoelectrically converting unit S.sub.G
and the photoelectrically converting unit S.sub.R of the pixels
with the green and red color filters are the same as that of the
photoelectrically converting unit S.sub.B of the pixel with the
blue color filter.
[0067] A pixel without a color filter has higher light receiving
efficiency than that of a pixel with a color filter, and the same
control operation for a storing time of charges causes saturation
thereof. Therefore, the sum of the areas of the first
photoelectrically converting unit S and the second
photoelectrically converting unit S.sub.W2 of the pixels without
the color filter are set to be smaller than the area of the
photoelectrically converting unit S.sub.B of the pixel with the
color filter
[0068] The light transmittance of a pixel with a color filter is
approximately 1/3 of that of a pixel without a color filter. If the
area of the first photoelectrically converting unit S.sub.W1 of the
pixel without a color filter is smaller than 1/3 of that of a
photoelectrically converting unit S.sub.B of the pixel with the
color filter, the output of a pixel without a color filter is
smaller than the output of a pixel with a color filter and a image
having a high S/N ratio for the subject with a low luminance cannot
be obtained.
[0069] Then, the area of the first photoelectrically converting
unit S.sub.W1 of a pixel without a color filter is set to 1/3 or
more of the area of the photoelectrically converting unit S.sub.B
of a pixel with a color filter, thus obtaining a preferable
image.
[0070] In summary, according to the second embodiment, the areas of
the first photoelectrically converting unit S.sub.W1, the second
photoelectrically converting unit S.sub.W2, the photoelectrically
converting unit S.sub.R, the photoelectrically converting unit
S.sub.G, and the photoelectrically converting unit S.sub.B are as
follows.
[0071] 3.times.S.sub.W1.gtoreq.S.sub.B=S.sub.G=S.sub.R
[0072] (S.sub.W1+S.sub.W2)<S.sub.B=S.sub.G=S.sub.R
[0073] FIG. 6 is a flowchart showing the sequence of the adjustment
of the luminance by the digital still camera 1 having the color
filters shown in FIG. 5B. Referring to FIG. 6, the sequence in step
S207 of the adjustment of the luminance mentioned with reference to
FIGS. 5A and 5B is shown.
[0074] The image pick-up operation in FIG. 4 is instructed (S207).
Then, the CPU 20 determines whether or not the luminance of the
subject is brighter than a predetermined threshold based on the
previously picked-up image (step S230).
[0075] When it is determined in step S230 that the luminance of the
subject is brighter than the predetermined threshold, it is
controlled so that in the pixel without a color filter, only
optical charges generated in the first photoelectrically converting
unit S.sub.W1 are output. As a result, saturation of the
photoelectrically converting outputs is further prevented in the
case of a bright subject and the image processing circuit 24 sets a
photoelectrically converting output Y.sub.W1 as a luminance signal
Y (step S231).
[0076] When it is determined in step S230 that the luminance of the
subject is darker than the predetermined threshold, it is
controlled so that optical charges generated in the first
photoelectrically converting unit S.sub.W1 and optical charges
generated in the second photoelectrically converting unit S.sub.W2
are added and output. As a result, The image processing circuit 24
sets the photoelectrically converting output (Y.sub.W1+Y.sub.W2) as
a luminance signal Y (step S233).
[0077] Then, the CPU 20 sends the signal to the image sensor
control circuit 21 and executes the image pick-up operation.
[0078] The color difference signal is generated by the output of
the pixel to which the "R", "G", and "B" color filters are formed.
The luminance signal is generated by the output of the pixel to
which the color filter is not formed.
[0079] A sensitivity I of the white color of the photoelectrically
converting unit of each pixel satisfies the following relationship,
based on the transmittance of the color filter and the area of the
photoelectrically converting unit.
[0080]
(I.sub.W1+I.sub.W2)>I.sub.W1.gtoreq.I.sub.B.congruent.I.sub.G.co-
ngruent.I.sub.R
[0081] Herein, reference numeral I.sub.B denotes the sensitivity of
the photoelectrically converting unit S.sub.B, reference numeral
I.sub.G denotes the sensitivity of the photoelectrically converting
unit S.sub.G, reference numeral I.sub.R denotes the sensitivity of
the photoelectrically converting unit S.sub.R, reference numeral
I.sub.W1 denotes the sensitivity of the first photoelectrically
converting unit S.sub.W1 and reference numeral I.sub.W2 denotes the
sensitivity of the second photoelectrically converting unit
S.sub.W2 which surrounds the first photoelectrically converting
unit S.sub.W1.
[0082] As mentioned above, when the luminance of the subject is
high, the luminance signal is determined based on only the output
Y.sub.W1 of the first photoelectrically converting unit S.sub.W1.
When the luminance of the subject is low, the luminance signal is
determined based on the output Y.sub.W1 of the first
photoelectrically converting unit S.sub.W1 and the output Y.sub.W2
of the second photoelectrically converting unit S.sub.W2. Thus, a
preferable image can be reproduced irrespective of the luminance of
the subject.
[0083] According to the first embodiment, when the luminance of the
subject is bright, the luminance signal is determined based on the
output Y.sub.W1 of the first photoelectrically converting unit
S.sub.W1. However, the luminance signal Y obtained from the output
of a pixel with a color filter may be added and the added luminance
signal may be determined.
[0084] (Third Embodiment)
[0085] FIG. 7 is a block diagram showing the schematic structure of
a digital still camera 1 according to a third embodiment of the
present invention. Referring to FIG. 7, reference numeral 52
denotes a driver for determining a value of the stop 53 to a
predetermined stop value, reference numeral 50 denotes a lens CPU
for controlling the operation of the lens driver 51 and the stop
driving means 52, and reference numeral 26 denotes an electrical
contact portion for intermediating information on the adjustment of
the focal point, which is sent from the CPU 20 to the lens CPU
50.
[0086] Referring to FIG. 7, the same components as those in FIG. 1
are designated by the same reference numerals. However, the memory
circuit 22 stores peculiar information (an F value of the opening
aperture, information on an exit window, etc.) of the photographing
lens 5. The photographing lens 5 is detachable to the main body of
the digital still camera 1.
[0087] FIG. 8 is a plan view showing the schematic structure of the
image sensor 10 in FIG. 7, corresponding to FIG. 2. Although pixels
having 12 rows and 8 columns are aligned in FIG. 8, the number of
pixels corresponding to the use is actually aligned.
[0088] Reference symbols "R", "G", and "B" denote the color phases
of red (R), green (G), and blue (B) color filters of the pixels.
Pixels having the same color are aligned with gird patterns to
improve the resolution of the picked-up image. Herein, the
arrangement is similar to the Bayer arrangement.
[0089] FIGS. 9A to 9C are enlargement views of pixels (2,0), (0,2),
and (1,0) in FIG. 8, corresponding to FIGS. 3A and 3B.
[0090] Referring to FIG. 9A, the pixel (2, 0) has the same
structure of that of the pixel (0, 0) shown in FIG. 3A. The areas
of the photoelectrically converting units S.sub.G and S.sub.R of
the pixels with the green and red color filters are the same as
that of the photoelectrically converting unit SB shown in FIG.
9A.
[0091] Referring to FIG. 9B, in the pixel (0, 2), two rectangular
photoelectrically converting unit S.sub.Wv long in the X direction
are aligned in the Y direction. A focusing state of the
photographing lens 5 is detected based on the outputs of the
photoelectrically converting units S.sub.Wv. In particular, the
detection of the focal point is preferably performed when the
subject includes a parallel line in the Y direction.
[0092] Referring to FIG. 9C, in the pixel (1, 0), two rectangular
photoelectrically converting unit S.sub.Wh long in the Y direction
are aligned in the X direction. The focusing state of the
photographing lens 5 is detected based on the outputs of the
photoelectrically converting units S.sub.Wh. In particular, the
detection of the focusing point is preferably performed when the
subject includes a parallel line in the X direction.
[0093] A gap between the photoelectrically converting units
S.sub.Wh is narrower than that between the photoelectrically
converting units S.sup.Wv. The area of the photoelectrically
converting units S.sub.Wh is wider than that between the
photoelectrically converting units S.sub.Wv.
[0094] Specifically, the area of each photoelectrically converting
unit satisfies the following relation.
[0095]
S.sub.B=S.sub.G=S.sub.R>2.times.S.sub.Wh>2.times.S.sub.Wv
[0096] The area of a photoelectrically converting unit of a pixel
without a color filter is set to be smaller than the area of a
photoelectrically converting unit of a pixel with a color filter,
thus preventing saturation of the photoelectrically converting unit
of the pixel without the color filter upon normal
photographing.
[0097] FIG. 10 is a cross sectional view of the image sensor 10 in
FIG. 7. FIG. 10 shows a CMOS image sensor. Incidentally, the cross
sectional view in FIG. 10 corresponds to the cross sectional view
of the pixels in FIGS. 9A to 9C.
[0098] Referring to FIG. 10, reference numeral 117 denotes a P-type
well, reference numeral 118 denotes an SiO.sub.2 film as an MOS
gate insulating film. Reference numerals 126.alpha..sub.0 to
126.gamma..sub.0 denote surface P.sup.+ layers, and form n-layers
125.alpha..sub.0 to 125.gamma..sub.0 and photoelectrically
converting units 101.alpha..sub.0 to 101.gamma..sub.0,
respectively.
[0099] Reference numerals 120.alpha..sub.0 to 120.gamma..sub.0 are
transfer gates for transferring optical charges stored in the
photoelectrically converting units 101.alpha..sub.0 to
101.gamma..sub.0 to floating diffusion units (hereinafter, referred
to as FD units) 121.alpha..sub.0 to 121.gamma..sub.0.
[0100] Further, reference numeral 129 denotes a color filter, and
reference numeral 130 denotes a micro lens. The micro lens 130 is
formed at a position and with a shape, in which the pupil of the
photographing lens 5 and the photoelectrically converting units
101.alpha..sub.0 to 101.gamma..sub.0 of the image sensor 10 are
conjugate.
[0101] In the pixel (1, 0), the photoelectrically converting units
101.alpha..sub.0 and 101.beta..sub.0 are formed by sandwiching the
FD unit 121.beta..sub.0. Further, the optical charges generated in
the photoelectrically converting units 101.alpha..sub.0 and
101.beta..sub.0 are transferred via the transfer gate
120.alpha..sub.0 and a transfer gate 120.beta..sub.0'.
[0102] In the pixel (2, 0), the FD unit 121.gamma..sub. is formed
between the photoelectrically converting units 101.gamma..sub.0 and
101.beta..sub.0. Further, the optical charges generated in the
photoelectrically converting units 101.gamma..sub.0 and
101.beta..sub.0 are transferred via the transfer gates
120.gamma..sub.0 and 120.beta..sub.0.
[0103] Herein, the transfer gates 120.gamma..sub.0 and
120.beta..sub.0' are controlled by the same control pulse
.PHI.TX.gamma..sub.0. The optical charges of the photoelectrically
converting unit 101.beta..sub.0 are selectively transferred to the
FD units 121.alpha..sub.0 and 121.gamma..sub.0 by high/low of
control pulses .PHI.TX.beta..sub.0 and
.PHI.TX.sub..gamma..sub.0.
[0104] FIG. 11 is a circuitry diagram including the image sensor 10
in FIG. 7. FIG. 11 shows four pixels (1, 0), (2, 0), (1, 1), and
(2, 1) in FIG. 8.
[0105] Referring to FIG. 11, reference numerals 103.alpha..sub.0 to
103.gamma..sub.0 denote transfer switch MOS transistors including
the transfer gates 120.alpha..sub.0 to 120.gamma..sub.0 in FIG. 10.
Reference numeral 104 denotes an MOS transistor for reset which
resets the FD units 121.alpha..sub.0 to 121.gamma..sub.0 and the
like to a predetermined potential. Reference numeral 105 denotes a
source follower amplifier MOS transistor for obtaining an
amplification signal based on the charges transferred by the
transfer switch MOS transistors 103.alpha..sub.0 to
103.gamma..sub.0. Reference numeral 106 denotes a horizontally
selecting switch MOS transistor which selects a read pixel of the
amplification signal obtained by the source follower amplifier MOS
transistor 105. Reference numeral 107 denotes a working MOS
transistor which forms a source follower together with the source
follower amplifier MOS transistor 105. Reference numerals
108.alpha..sub.0 and 108.beta..sub.0 denote dark output transfer
MOS transistors which transfer a dark output of the pixel.
Reference numerals 109.alpha..sub.0 and 109.beta..sub.0 denote
bright output transfer MOS transistors which transfer a bright
output of the pixel. Reference numerals 110.alpha..sub.0 and
110.beta..sub.0 denote storage capacitors of the dark output for
storing the dark output transferred by the dark output transfer MOS
transistors 108.alpha..sub.0 and 108.beta..sub.0. Reference numeral
111.alpha..sub.0 and 111.beta..sub.0 denote storage capacitors of
the bright output for storing the bright output transferred by the
bright output transfer MOS transistors 109.alpha..sub.0 and
109.beta..sub.0. Reference numerals 112.alpha..sub.0 and
112.beta..sub.0 denote horizontally transfer MOS transistors which
transfer the outputs stored in the storage capacitors
110.alpha..sub.0 and 110.beta..sub.0 of the dark output and the
storage capacitors 111.alpha..sub.0 and 111.beta..sub.0 of the
bright output. Reference numeral 113 denotes a horizontal output
line reset MOS transistor which resets a horizontal output line to
a predetermined potential. Reference numeral 114 denotes a
difference output amplifier which amplifies and outputs the
difference between the signals transferred along the horizontal
output line. Reference numeral 115 denotes a horizontal scanning
circuit which controls the on/off operation of the horizontally
transfer MOS transistors 112.alpha..sub.0 and 112.beta..sub.0.
Reference numeral 116 denotes a vertical scanning circuit which
controls the on/off operation of the transfer switch MOS
transistors 103.alpha..sub.0 to 103.gamma..sub.0.
[0106] FIGS. 12A and 12B are timing charts showing the operation of
circuits in the image sensor 10 in FIG. 11. FIG. 12A shows a timing
chart of a 0-th line in the case of normal image pick-up operation.
FIG. 12B shows a timing chart of the 0-th line in the case of
reading the image for detecting the focal point.
[0107] In summary, the image pick-up operation will be described.
In the pixel (1, 0), the charges converted by the photoelectrically
converting units 101.alpha..sub.0 and 101.beta..sub.0 are
transferred to the FD unit 121.alpha..sub.0. The charges are added
by the FD unit 121.alpha..sub.0 and are read. In this case, in the
pixel (2, 0), the charges converted by the photoelectrically
converting unit 101.gamma..sub.0 are transferred to the FD unit
121.gamma..sub.0 and are read.
[0108] The image pick-up operation will specifically be described
with reference to FIG. 12A. First, a control pulse .PHI.S.sub.0 is
switched to the high level by a timing output from the vertical
scanning circuit 116. The horizontally selecting switch MOS
transistor 106 is turned on and the pixel portion in the 0-th line
is selected.
[0109] Next, a control pulse .PHI.R.sub.0 is switched to the low
level. The reset operation of the FD units 121.alpha..sub.0 and
121.gamma..sub.0 is stopped, thereby setting the FD units
121.alpha..sub.0 and 121.gamma..sub.0 to be in a floating state. A
gate of the source follower amplifier MOS transistor 105 is through
a source thereof. Then, after a predetermined time, a control pulse
.PHI.TN is temporarily switched to the high level. Thus, dark
voltages of the FD units 121.alpha..sub.0 and 121.gamma..sub.0 are
outputted to the storage capacitors 110.alpha..sub.0 and
110.beta..sub.0 of the dark output by the source follower
operation.
[0110] Next, control pulses .PHI.TX.alpha..sub.0 and
.PHI.TX.gamma..sub.0 are temporarily switched to the high level so
as to output the charges from the photoelectrically converting
units 101.alpha..sub.0 to 101.gamma..sub.0 of the pixels of the
0-th line, and the transfer switch MOS transistors
103.gamma..sub.0, 103.beta..sub.0' and 103.gamma..sub.0 are made
conductive.
[0111] The charges converted by the photoelectrically converting
units 101.alpha..sub.0 and 101.beta..sub.0 are transferred to the
FD unit 121.alpha..sub.0. The charges converted by the
photoelectrically converting unit 101.gamma..sub.0 are transferred
to the FD unit 121.gamma..sub.0.
[0112] The charges from the photoelectrically converting units
101.alpha..sub.0 and 101.beta..sub.0 are transferred to the FD unit
121.alpha..sub.0. Thus, the potential of the FD unit
121.alpha..sub.0 is changed in accordance with the light. In this
case, the source follower amplifier MOS transistor 105 is set to be
in the floating state. Therefore, the potentials of the FD units
121.alpha..sub.0 and 121.gamma..sub.0 are output to the storage
capacitors 111.alpha..sub.0 and 111.beta..sub.0 of the bright
output by temporarily setting a control pulse 101 TS to the high
level.
[0113] At this point, the dark output and bright output of the
pixels (1, 0) and (2, 0) are stored in the storage capacitors
110.alpha..sub.0 and 110.beta..sub.0 of the dark output and the
storage capacitors 111.alpha..sub.0 and 111.beta..sub.0 of the
bright output. Further, the control pulse .PHI.HC is temporarily
switched to the high level and the horizontal output line reset MOS
transistor 113 is made conductive, thereby resetting the horizontal
output line.
[0114] The dark output and bright output of the pixels (1, 0) and
(2, 0) are output to the horizontal output line by sending scanning
timing signals to the horizontal transfer MOS transistors
112.alpha..sub.0 and 112.beta..sub.0 from the horizontal scanning
circuit 115 for the horizontal transfer period.
[0115] In this case, signals from the storage capacitors
110.alpha..sub.0 and 110.beta..sub.0 of the dark output and the
storage capacitors 111.alpha..sub.0 and 111.beta..sub.0 of the
bright output are amplified by the difference of the difference
amplifier 114 and generate an output Vout. Therefore, it is
possible to obtain a signal having a preferable S/N ratio excluding
random noise of the pixel and a fixed pattern noise.
[0116] Thereafter, the control pulse .PHI.R.sub.0 is switched to
the high level, and the control pulse .PHI.S.sub.0 is switched to
the low level, thereby ending the selection of the pixels of the
0-th line.
[0117] Further, similarly, the vertical scanning circuit 116
sequentially reads the charges from the pixels of the next line,
thereby outputting the signals from all the pixels of the image
sensor 10. The output is subjected to signal processing by the
image processing circuit 24 and is displayed on the liquid crystal
display device 9. Then, the image is stored in the memory circuit
22.
[0118] The outline of the detection of the focal point will be
described. Two images obtained from the outputs of the
photoelectrically converting units 101.alpha..sub.0 and
101.beta..sub.0 are subjected to correlative calculation. The
focusing state of the photographing lens 5 is detected from the
amount of offset between the two images.
[0119] The output of the photoelectrically converting unit
101.gamma..sub.0 is not read. The output of the photoelectrically
converting unit 101.gamma..sub.0 is output from the pixel (2,
0).
[0120] The operation for detecting the focusing state will
specifically be described with reference to FIG. 12B. First, the
control pulse .PHI.S.sub.0 is switched to the high level by a
timing output from the vertical scanning circuit 116. The
horizontally selecting switch MOS transistor 106 is turned on and
the pixel portion in the 0-th line is selected.
[0121] Next, the control pulse .PHI.R.sub.0 is switched to the low
level. The reset operation of the FD units 121.alpha..sub.0 and
121.gamma..sub.0 is stopped, thereby setting the FD units
121.alpha..sub.0 and 121.gamma..sub.0 to be in the floating state.
The gate of the source follower amplifier MOS transistor 105 is
through the source thereof. Then, after a predetermined time, the
control pulse .PHI.TN is temporarily switched to the high level.
Thus, dark voltages of the FD units 121.alpha..sub.0 and
121.gamma..sub.0 are output to the storage capacitors
110.alpha..sub.0 and 110.beta..sub.0 of the dark output by the
source follower operation.
[0122] Next, the control pulses .PHI.TX.alpha..sub.0 and
.PHI.TX.beta..sub.0 are temporarily switched to the high level,
thereby making the transfer switch MOS transistors 103.alpha..sub.0
and 103.beta..sub.0 conductive. The charges converted by the
photoelectrically converting units 101.alpha..sub.0 and
101.beta..sub.0 are transferred to the FD units 121.alpha..sub.0
and 121.alpha..sub.0.
[0123] In this case, the control pulse .PHI.TX.gamma..sub.0 is low
and therefore the optical charges of the photoelectrically
converting unit 101.gamma..sub.0 are not transferred to the FD unit
121.gamma..sub.0.
[0124] The charges from the photoelectrically converting units
101.alpha..sub.0 and 101.beta..sub.0 are transferred to the FD
units 121.alpha..sub.0 and 121.gamma..sub.0. Thus, the potentials
of the FD unit 121.alpha..sub.0 and 121.gamma..sub.0 are changed in
accordance with the light. In this case, the source follower
amplifier MOS transistor 105 is set to be in the floating state.
Therefore, the potentials of the FD units 121.alpha..sub.0 and
121.gamma..sub.0 are output to the storage capacitors
111.alpha..sub.0 and 110.beta..sub.0 of the bright output by
temporarily setting the control pulse .PHI.TS to the high
level.
[0125] In this case, the dark output and bright output of the
pixels (1, 0) and (2, 0) are stored in the storage capacitors
110.alpha..sub.0 and 110.beta..sub.0 of the dark output and in the
storage capacitors 111.alpha..sub.0 and 111.beta..sub.0 of the
bright output. Further, the control pulse .PHI.HC is temporarily
switched to the high level. Thus, the horizontal output line reset
MOS transistor 113 is made conductive and the horizontal output
line is reset.
[0126] The dark output and light output of the pixels (1, 0) and
(2, 0) are output to the horizontal output line by sending scanning
timing signals to the horizontal transfer MOS transistors
112.alpha..sub.0 and 112.beta..sub.0 from the horizontal scanning
circuit 115 for the horizontal transfer period.
[0127] In this case, signals from the storage capacitors
110.alpha..sub.0 and 110.beta..sub.0 of the dark output and the
storage capacitors 111.alpha..sub.0 and 111.beta..sub.0 of the
bright output are amplified by the difference of the difference
amplifier 114 and generate an output Vout. Therefore, a signal
having a preferable S/N ratio excluding the random noise of the
pixel and the fixed pattern noise.
[0128] Thereafter, the control pulse .PHI.R.sub.0 is switched to
the high level, and the control pulse .PHI.S.sub.0 is switched to
the low level, thereby ending the selection of the pixels of the
0-th line.
[0129] The output from the image sensor 10 is shaped as an image
signal for detecting the focal point by the calculation of the CPU
20. After the correlation calculation, the focal point of the
photographing lens 5 is calculated.
[0130] FIG. 13 is a flowchart showing the operation of the digital
still camera 1 in FIG. 7.
[0131] The photographing person switches on the main switch of the
digital still camera 1 (not shown in FIG. 7) (step S301). The CPU
20 performs the calculation for detecting the focal point of the
photographing lens 5.
[0132] The focal point of the photographing lens 5 is detected by
using the output of the image sensor 10. A method for detecting the
focusing state of the photographing lens 5 using the image
generated by the beams for transmitting the different areas of the
pupil of the photographing lens 5 uses the method disclosed in
Japanese Unexamined Patent Application Publication No. 2001-124984
(step S302).
[0133] The amount of defocusing of the photographing lens 5 is
calculated based on the output of the image sensor 10. Then, the
amount of driving of the photographing lens 5 is calculated. The
CPU 20 sends a lens driving signal to the photographing lens
driving means 51 via the lens CPU 50 based on the calculation
result. The photographing lens driving means 51 drives the
photographing lens 5 in accordance with the lens driving signal so
as to set the photographing lens 5 in the in-focus state (step
S303).
[0134] When the adjustment of the focal point of the photographing
lens 5 is completed, the CPU 20 allows the image sensor 10 to pick
up the image via the image sensor control circuit 21 (step
S304).
[0135] The image signal picked up by the image sensor 10 is
subjected to image processing after it is A/D converted by the
image processing circuit 24. In this case, predetermined image
processing is performed based on the output signal from the image
sensor 10 for purpose of the color reproduction.
[0136] The image signal which is subjected to image processing is
displayed on the liquid crystal display device 9 by the liquid
crystal display device driving circuit 25 so as to permit the
photographs to observe the subject image via the eye piece 3 (step
S305).
[0137] Further, the CPU 20 switches on the switch SW2 for recording
the picked-up image (step S306). Then, the CPU 20 sends the control
signal to the image sensor control circuit 21, and the image sensor
10 performs the actual image pickup operation (step S307).
[0138] The image processing circuit 24 sends to the liquid crystal
display device driving circuit 25, the image generated by the image
processing including the adjustment of luminance, which will be
described later, and it displays the sent image on the liquid
crystal display device 9 (step S308).
[0139] Simultaneously, the CPU 20 stores the picked-up image signal
in the memory circuit 22 in the digital still camera 1 (step
S309).
[0140] The photographing operation ends and the photographing
person switches off the main switch (step S310). Then, the power
source of the digital still camera 1 is turned off.
[0141] Upon adjustment of the luminance, only the charges from the
pixels of one line may be read. Preferably, the line for reading
the charges is approximately in the center of the image sensor 10
in consideration of condensing characteristics of the photographing
lens 5.
[0142] FIG. 14 is a flowchart showing the sequence for calculating
the luminance signal for adjusting the luminance by the image
processing circuit 24 in FIG. 7, corresponding to FIG. 6. Further,
FIG. 14 shows the above-mentioned sequence for determining the
luminance signal Y of the image in step S307.
[0143] According to the third embodiment, the color difference
signal is generated from the outputs of the pixels with the "R",
"G", and "B" color filters, and the luminance signal Y is generated
by the output of the pixels without color filters.
[0144] The sensitivity I for the white light of each pixel
satisfies the following relation based on the areas of the
photographing converting units and the transmittances of the color
filters.
2>I.sub.Wh>I.sub.B.congruent.I.sub.G.congruent.I.sub.R.gtoreq.2.time-
s.I.sub.Wv
[0145] Herein, reference numeral I.sub.B denotes the sensitivity of
the photoelectrically converting unit S.sub.B. Reference numeral
I.sub.G denotes the sensitivity of the photoelectrically converting
unit S.sub.G. Reference numeral I.sub.R denotes the sensitivity of
the photoelectrically converting unit S.sub.R. Reference numeral
I.sub.Wh denotes the sensitivity of the photoelectrically
converting unit S.sub.Wh. Reference numeral I.sub.Wv denotes the
sensitivity of the photoelectrically converting unit S.sub.Wv.
[0146] The luminance signal as a basic unit of the image consisting
of the pixels (0, 0), (1, 0), (0, 1), and (1, 1) shown in FIG. 8 is
determined based on an output Yh of the pixel (1, 0) and an output
Yv of the pixel (0, 2).
[0147] First, the image processing circuit 24 determines whether or
not the output Yh of the pixel (1, 0) is larger than a
predetermined threshold Ythh (step S320).
[0148] If the luminance of the subject is bright and the output Yh
of the pixel is larger than the threshold Ythh, the luminance
signal Y is set to the output Yv of the pixel (0, 2) (step
S321).
[0149] On the other hand, if the output Yh of the pixel is smaller
than the threshold Ythh, it is determined whether or not the output
Yv of the pixel (0, 2) is smaller than the threshold Ythv (step
S322).
[0150] If the luminance of the subject is dark and the output of
the pixel Yv is smaller than the threshold Ythv, the luminance
signal Y is set to the output Yh of the pixel (1, 0) (step
S323).
[0151] On the other hand, if the output Yv of the pixel is larger
than the threshold Ythv, the luminance signal Y is set to the
average between the output Yh of the pixel (1, 0) and the output Yv
of the pixel (0, 2) (step S324).
[0152] As mentioned above, when the luminance of the subject is
higher, the luminance is determined based on the output Yv of the
photoelectrically converting unit S.sub.Wv with a relatively small
area. When the luminance of the subject is lower, the luminance is
determined based on the output Yh of the photoelectrically
converting unit S.sub.Wh with a relatively large area. Thus, the
image can preferably be reproduced irrespective of the luminance of
the subject.
[0153] According to the third embodiment, the case of adjusting the
luminance based on the outputs of the pixels (1, 0) and (0, 2) is
described. However, the luminance may be adjusted, based on a pixel
having the same structure as that of the above-mentioned pixels and
the outputs of a plurality of pixels.
[0154] Further, the luminance may be adjusted based on the output
of the single photoelectrically converting unit. Also, the
luminance may be adjusted in consideration of the output of the
pixel with the color filter of the pixel (0, 1), etc.
[0155] According to the first to third embodiments, the case of
physically converting the area of the photoelectrically converting
unit is described. However, the size of the photoelectrically
converting area on which the optical signal is incident may be
changed by setting the areas of the photoelectrically converting
units to be the same and by forming shielding films having
different opening regions.
[0156] Furthermore, according to the first to third embodiments, a
part of the pixels without the color filter is described. However,
an almost transparent color filter with exceedingly high
transmittance may be arranged in a part of the pixels.
[0157] As mentioned above, according to the first to third
embodiments, a pixel for an image pick-up operation and a pixel for
detecting the focal point are provided and therefore both the image
pick-up operation and the detection of the focal point can
preferably be performed.
[0158] While the present invention has been described with
reference to what are presently considered to be the preferred
embodiments, it is to be understood that the invention is not
limited to the disclosed embodiments. On the contrary, the
invention is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended
claims. The scope of the following claims is to be accorded the
broadest interpretation so as to encompass all such modifications
and equivalent structures and functions.
* * * * *